This invention relates in general to electrophotographic imaging members and more specifically, to a process for fabricating an electrophotographic imaging member having an improved charge generation layer.
In the art of electrophotography an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the imaging surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable electrophotographic imaging members.
The electrophotographic imaging members may be in the form of plates, drums or flexible belts. These electrophotographic members are usually multilayered photoreceptors that comprise a substrate, a conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer, an optional overcoating layer and, in some belt embodiments, an anti-curl backing layer.
A conventional technique for coating cylindrical or drum shaped photoreceptor substrates involves dipping the substrates in coating baths. The bath used for preparing photoconducting layers is prepared by dispersing photoconductive pigment particles in a solvent solution of a film forming binder. Unfortunately, some organic photoconductive pigment particles cannot be applied by dip coating to form high quality photoconductive coatings. For example, organic photoconductive pigment particles such benzimidazole perylene pigments tend to settle when attempts are made to disperse the pigments in a solvent solution of a film forming binder. The tendency of the particles to settle requires constant stirring which can lead to entrapment of air bubbles that are carried over into the final photoconductive coating deposited on a photoreceptor substrate. These bubbles cause defects in final prints xerographically formed with the photoreceptor. The defects are caused by differences in discharge of the electrically charged photoreceptor between the region where the bubbles are present and where the bubbles are not present. Thus, for example, the final print will show dark areas over the bubbles during discharged area development or white spots when utilizing charged area development. Moreover, many pigment particles tend to agglomerate when attempts are made to disperse the pigments in solvent solutions of film forming binders. The pigment agglomerates lead to non-uniform photoconductive coatings which in turn lead to other print defects in the final xerographic prints due to non-uniform discharge.
In addition, some dispersions react non-uniformly when deposited as a coating on a photoreceptor substrate to form discontinuous coatings during dip coating or roll coating operations. It is believed that these discontinuous coatings are caused by the coating material flowing in some regions of the coating and not in other regions.